1. Field of the Invention
The present invention relates to an Internet group membership protocol (IGMP) network device and a signal processing control method thereof in an Internet protocol (IP) digital broadcasting system.
2. Description of the Related Art
In general, an Internet protocol television, i.e., an IP TV provides information service, moving picture content, and broadcasting on television using ultra-high speed Internet. The IP TV is a type of digital convergence based on a combination of Internet and television, and is different from a conventional Internet TV in that a television receiver is substituted for a computer monitor and a remote controller is substituted for a mouse.
To use the IP TV, a television receiver, a set-top box, and Internet can be connected. In other words, the IP TV can be used when the set-top box or a dedicated modem is added to the television and power is applied as the television turns on. Accordingly, though not familiar to a computer, a user can be provided with various Internet providing contents such as movie viewing, home shopping, home banking, online game, MP3, and additional services thereof as well as Internet search using a remote controller.
The IP TV does not have a great difference from general cable broadcasting or satellite broadcasting in that it provides broadcasting content including video, but has a great feature in bidirectionality. Unlike general sky wave broadcasting, cable broadcasting, or satellite broadcasting, a viewer can view only his/her program desired at his/her convenient time. Accordingly, the initiative of TV broadcasting is given to the viewer from a broadcasting company or a relay company. At present, the IP TV service is being provided in some countries such as Hong Kong, Italy, and Japan, but is at an initial stage all over the world. In the interior, communication service providers are actively providing the IP TV to have an economic effect of scopes using a given infrastructure to the maximum.
An IP TV system includes at least one IGMP client including a TV receiver and an IP set-top box, and network devices allowing the IGMP clients to receive the IP TV service over the Internet. The network device is composed of a host (CPU) for processing an IGMP request of the IGMP client (subscriber); and a packet transmission/reception unit connected to the IGMP client over the Internet and connected to an upper IGMP network device to take charge of a data transmission/reception function. Each of the host and the packet transmission/reception unit has a multicast table for storing channel information (group IP or group media access control (MAC)) and IGMP client information on a channel-by-channel basis, creates/modifies/deletes the multicast table as a result of processing an IGMP packet and, if necessary, creates a proper IGMP packet and transmits the created IGMP packet to the upper IGMP network device.
In the IGMP network device, the IGMP processing is wholly dependent on the host and therefore, the IGMP network device provides a plan for reducing the number of IGMP packets transmitted to the upper IGMP network device. In other words, it is a method in which a necessary one of the IGMP packets received from the IGMP client or only an IGMP message created by the host is transmitted to the upper IGMP network device, thereby reducing host load of the upper IGMP network device. This function is called “report suppression”. The IGMP network device has provided the function only on the basis of processing by the host.
A signal processing procedure of the conventional IGMP network device of the IP TV system providing the above function will be described below. In order to watch a predetermined channel (Ch 10), the IGMP client transmits an IGMP membership report (“report”) message to the packet transmission/reception unit of the IGMP network device. After that, the packet transmission/reception unit of the IGMP network device transmits the received IGMP report message to the host. Then, the host determines whether or not a channel requested by the IGMP client using the IGMP report message is registered in the multicast table.
When it is determined that the channel requested by the IGMP client is not registered in the multicast table, the host registers the channel requested by the IGMP client and the IGMP client information in the multicast table. The host also updates the multicast table of the packet transmission/reception unit to correspond to a change of the host.
After that, the host transmits the IGMP report message to the upper IGMP network device through the packet transmission/reception unit. The host can transmit the IGMP report message received from the IGMP client without any change, or transmit the received IGMP report message after modification.
Upon receipt of the IGMP report message requesting a predetermined channel from a lower IGMP network device, the upper IGMP network device determines whether or not a channel associated with the IGMP report message is received from an IP broadcasting station.
When it is determined that the channel requested using the IGMP report message is received from the IP broadcasting station, the upper IGMP network device copies and transmits an IP TV broadcasting stream of the requested channel to a packet transmission/reception unit of the lower IGMP network device. Otherwise, the upper IGMP network device is associated with a multicast routing protocol such as protocol independent multicast (PIM) and then receives a corresponding IP TV broadcasting stream, or again transmits the IGMP message to its upper network device to request an IP TV broadcasting stream and then transmits it to the packet transmission/reception unit of the lower IGMP network device.
If so, the packet transmission/reception unit of the lower IGMP network device transmits the IP TV broadcasting stream of the channel that is requested by the IGMP client transmitting the IGMP report message.
Meanwhile, when the channel requested by the IGMP client is registered in the multicast table of the packet transmission/reception unit, and the IGMP client is also registered on the channel, the host updates the IGMP client information to the channel registered in the multicast table and terminates.
However, when the channel requested by the IGMP client is registered in the multicast table of the packet transmission/reception unit and the IGMP client is not registered on the channel, the host adds the IGMP client information to the channel registered in the multicast table, and allows the added IGMP client information to be reflected to the packet transmission/reception unit. After that, the IP TV stream of the channel is copied and transmitted even to the IGMP client.
In the conventional IP TV system, the IGMP client generates the IGMP packets to watch the TV, and transmits the generated IGMP packets to the network device receiving the IP TV stream, through at least one IGMP network device. Not only when the channel changes but also in order to keep watching one channel, the IGMP client periodically generates the IGMP packets. Therefore, as the IGMP clients connected to an IP TV network increase in number, the whole generated IGMP packets also increase in number.
Since the IGMP packets generated to choose a TV channel by the IGMP clients are processed in the host of the IGMP network device, the hosts of the respective network devices are delayed due to the processing and this results in an increase of a standby time for channel change of the IGMP client.